Steve Bannon found himself abandoned last week — in a span of fewer than 30 hours — by two key forces that had fueled his rise and made his kingmaker image.

President Donald Trump broke ties with Bannon on Wednesday, saying the former White House chief strategist had “lost his mind” following the release of book excerpts that showed Bannon called a meeting between Donald Trump Jr. and Russian contacts “treasonous.”

Megadonor Rebekah Mercer then rejected him the next day and sided with Trump, dealing a blow perhaps even more damaging than the president’s.

The daughter of Robert Mercer, the Long Island billionaire who in 2016 put more than $22 million toward mostly conservative causes, in a rare public statement said she shut off the spigot to Bannon.

“That could be the final nail in his coffin,” said Rep. Peter King (R-Seaford), who for months has criticized Bannon as detrimental to the GOP. “And once that coffin’s closed, it shouldn’t be opened.”

Bannon and the Mercer family of Head of the Harbor had aligned during the 2016 campaign to run and finance a populist operation that boosted Trump to victory. They also jointly led a handful of influential operations, including right wing Breitbart News and data company Cambridge Analytica.

“Losing your primary financial backer is a catastrophic and devastating loss — particularly in politics, where money gives you power,” former Breitbart spokesman Kurt Bardella said of the Mercers. “He’s a man alone on an island.”

Interviews with nationalist activist Bannon are the backbone of “Fire and Fury: Inside the Trump White House” by Michael Wolff, who portrays the president as unfit to lead and unwilling to learn. Trump, in the book, is said to be like a “child” and “semiliterate” by people who work for the president.

Bannon has not denied the many unflattering descriptions he makes about Trump and his children. But he called the president a “great man” Wednesday on a Sirius XM show put on by Breitbart, where he is executive chairman.

Rebekah Mercer appeared to reference Bannon’s remarks in the book when she said her family “has provided no financial support to his political agenda, nor do we support his recent actions and statements.”

In November, Robert Mercer distanced himself from Bannon in a letter that announced Mercer’s retirement from his East Setauket hedge fund. He sold his Breitbart stakes to his daughters.

The Mercers and other Breitbart board members were debating last week whether to oust Bannon, The Wall Street Journal reported.

Rebekah Mercer stopped communicating with Bannon three or four months ago, a person familiar with their relationship told Newsday on the condition of anonymity.

There was the tension caused by personality clashes as well as more substantive issues, the person said, as the split came before Bannon-backed Roy Moore lost the Alabama Senate special election.

Christopher Ruddy, a Trump ally and chairman of the right-leaning Newsmax, told Newsday he doesn’t know of “one conservative” who would choose Bannon over Trump.

“Ultimately, I think he’s been toying with the idea of running for president and he wanted the president out of the White House,” Ruddy said.

Candidates endorsed by Bannon in the 2018 races also are distancing themselves from him, though to varying degrees.

A press secretary for Kelli Ward, a Republican candidate for the Senate race in Arizona, downplayed her ties to Bannon and called him “only one of many high-profile endorsements.”

Katie Vincentz, communications director for Rep. Lee Zeldin (R-Shirley), gave no indication that Zeldin was about to turn his back on Bannon.

“Hopefully Mr. Bannon is going to be able to clarify whether this book accurately describes what he said,” she said.

Zeldin’s campaign raised an “eye-popping” amount in a Manhattan event that Bannon headlined last month, according to a person familiar with planning, speaking on the condition of anonymity.

In a statement, Michael Grimm, a Republican mounting a congressional comeback bid in Staten Island, called the “baseless attacks against the President’s family, beyond disturbing,” adding, “I fully support our commander in chief.”